Equity method investment - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Schedule of Equity Method Investments [Line Items]
Technology, trade name and customer relationship intangibles	$ 44,713,000		$ 44,713,000		$ 51,130,000
Amortization of Intangible Assets	2,417,000	$ 2,430,000	7,416,000	$ 7,012,000
Dividends received from equity method investment			47,981,000	49,940,000
Bankers Healthcare Group, LLC
Schedule of Equity Method Investments [Line Items]
Technology, trade name and customer relationship intangibles	7,900,000		7,900,000		$ 8,800,000
Amortization of Intangible Assets	293,000	475,000	880,000	1,400,000
Accretion income	535,000	630,000	1,600,000	2,000,000.0
Dividends received from equity method investment	40,000,000.0	9,000,000.0	48,000,000.0	49,900,000
Payments to Acquire Loans Held-for-investment	$ 50,200,000	$ 0	$ 50,200,000	$ 0